What is the meaning of the "yellow wood" in Robert Frost's poem "The Road Not Taken?"

The meaning of the ‘yellow wood’ is ambiguous and often misinterpreted, as is indeed, the meaning of the whole poem. Critics often propose that the ‘yellow wood’ suggests autumn with the association of  middle or old age, however, this is unlikely because the persona (person speaking) must be fairly young since he says that he will recall his choice of road ‘…ages and ages hence’.  Frost was good friends with another poet, Edward Thomas, who was plagued with indecision. It is possible that Frost wrote this poem thinking of his friend, even mocking him, and that the ‘yellow’ of the wood symbolizes the literary links with cowardice, or timidity – you might have heard a coward described as a ‘yellow dog’. Therefore, perhaps Frost is suggesting that Thomas could not decide on which road to take in life – whether to go and fight in the Great War in France, or whether to follow Frost back to America. If we follow this argument to its conclusion, we can understand that the persona is thus demonstrating the difficulties we all face when making decisions and in this lies the universal appeal of the metaphorical 'yellow wood'. 

The symbolism of yellow has many possible interpretations in this poem.
As the previous educator mentioned, the narrator is reflecting on the road he did not choose that autumn morning. Yellow and gold are also colors associated with morning and the rising sun. The reference to "a yellow wood" can represent both the autumn leaves and the dappled, golden sunlight falling on the forest floor.
Mornings are usually metaphors for new possibilities and new beginnings. The narrator's ability to choose is associated with a time in which his life offered more than one possibility—each fresh and equally attractive:

And both that morning equally layIn leaves no step had trodden black.

Like so many of us, he hoped for the chance to explore the other possibility: "Oh, I kept the first for another day!" But accepted that making one choice excludes the exploration of the other:

Yet knowing how way leads on to way,I doubted if I should ever come back. 

The narrator predicts that one day, "[s]omewhere ages and ages hence," during his "autumn" years, perhaps, he will remember his choice of the road "less traveled by," though it was "just as fair" as the other. The "difference" lies in the fact that his life would have been altogether different had he chosen the other path on that fateful morning. 
Thus the "yellow wood" represents possibility and a new beginning.

The “yellow wood” in Robert Frost’s poem “The Road Not Taken” provides details about its setting and tone. The setting for a number of Frost’s poems, including this one, is the state of New Hampshire. During the New England autumn, the leaves on the trees turn colors, including yellow. In this poem, the “yellow wood” speaks to the time of year and the type of day it is. The traveler comes upon the divergence in the path on an autumn morning when the golden sun is shining through the leaves. Some of the autumn leaves fell off the trees onto the paths below, which speaks to the movement of time.

And both that morning equally lay
In leaves no step had trodden black.

The color yellow is associated with thoughtfulness and intellect. The traveler’s decision weighs heavily upon him; he thinks deeply about which path to take.
Autumn symbolizes the passage of time as the year moves into its barren seasons. Although the traveler says he will keep the unclaimed path for another day, he seems to know he will not be back, and he will look upon the scene retrospectively. Those symbolic “yellow woods” will return to him in the autumn of his life—his golden years.